Barry Allen (aka The Flash) currently runs at a speed of 670,616,629 mph!
That's about 99.99999999999999982775% the speed of light
Explanation:
Season 4 episode 15 Barry tries to stop a already detonated nuke by freezing time and zooming back and forth throughout the city, tossing lightning, and even trying to freeze it, but still nothing works out. So then, Iris, Barry's wife tells Barry to run into the speed force and grab the genetic DNA ball so that the speed force's lightning would chase Barry into the nuke. Barry does so by running in and out of the speed force in a mater of seconds while the lightning pursues him. In the end he outraced lightning in Flashtime, becoming the fastest man ever to walk or live on the earth.
